Programming the Intel MCS-48 Microcontrollers

The Intel series of MCS-48 family of microcontrollers, commonly known as the 8048 series were one of the most prominent microcontrollers 35 years back. All they feature is 64 bytes of RAM, and access to 4096 bytes of external program memory.

The first thing was to make sure that an EEPROM was loaded with the program; however they supported the D27256 series of eeprom instead of D2758 series. To solve the problem upper addressable bits were tied to ground and the solution worked. The program was written in assembly with Windows 7 as the developing platform since the programming tools are running on the Windows platform.

Early Intel processors combine the address and data bits onto the same lines and use two signals: ALE (Address Latch Enable) and PSEN (Program Store Enable) to signal what state the bus is in. This was done to save costs and keep pin count down. Unfortunately this complicates the connection to an external PROM. To solve the problem Andrew Rossignol used an external latch to store the address lines after the bus returned to a floating state.